The present invention relates to magnetic coupling communication technique for transmitting signals using magnetic coupling via a transformer.
In the field of near-field contactless communication there is known a communication that uses magnetic coupling via a transformer (hereinafter referred to as “magnetic coupling communication”). In such a type of communication system, the transformer includes coils, each coil including an inductor. A transmission side transmits transmission data to a receiving side by transmitting transmission pulses that drive the inductor, with a pulse interval according to the data rate of the transmission data.
FIG. 17 shows the relation of transmission data, transmission pulses, and signals received by the receiving side (received signal) in a magnetic coupling communication system.
In FIG. 17, Rb represents the data rate of the transmission data. As shown in FIG. 17, a value 1 or 0 is treated as a single data symbol in the magnetic coupling communication system, the transmission interval (pulse interval) of data symbols being “1/Rb”. The transmission side outputs transmission pulses according to the value of the transmission data. As illustrated, with regard to the wave shape of the transmission pulse, the amplitude becomes large at the positive side for the transmission data of the value 1, whereas the amplitude becomes large at the negative side for the transmission data of the value 0. Additionally, with regard to the received signal, an amplitude arises corresponding to the leading edge of the transmission pulse, and distortion occurs in the received signal since a predetermined time is required for the amplitude to settle. The above-described predetermined time is determined by the self-resonant frequency of the inductors at the transmitting and receiving sides.
FIG. 18 shows the relation between the data rate Rb and the resonance frequency fL of the inductor in a conventional magnetic coupling communication system. As shown in FIG. 18, it is known that the data rate Rb is limited to equal to or lower than about 1/3 of the self-resonant frequency of the inductor for the conventional communication system in order to prevent interference between data symbols due to distortion of the wave shape of the received signal (Non-Patent Document 4: S. Kawai, H. Ishikuro, and T. Kuroda, “A 2.5 Gb/s/ch 4PAM inductive-coupling transceiver for non-contact memory card”, 2010 IEEE International Solid-State Circuits Conference Digest of Technical Papers (ISSCC), 2010, pp. 264-265.).
There have been proposed a variety of techniques for increasing the communication speed in a magnetic coupling communication system (Non-Patent Document 1: N. Miura, D. Mizoguchi, M. Inoue, K. Niitsu, Y. Nakagawa, M. Tago, M. Fukaishi, T. Sakurai, and T. Kuroda, “A 1 Tb/s 3 W inductive-coupling transceiver for 3D-stacked inter-chip clock and data link”, IEEE Journal of Solid-State Circuits, vol. 42, 2007, pp. 111-122, Non-Patent Document 2: N. Miura, D. Mizoguchi, M. Inoue, T. Sakurai, and T. Kuroda, “A195-Gb/s 1.2-W inductive inter-chip wireless superconnect with transmit power control method for 3-D-stacked system in a package”, IEEE Journal of Solid-State Circuits, vol. 41, 2006, p. 23, Non-Patent Document 3: N. Miura, D. Mizoguchi, T. Sakurai, and T. Kuroda, “Analysis and design of inductive coupling and transceiver circuit for inductive inter-chip wireless superconnect”, IEEE Journal of Solid-State Circuits, vol. 40, 2005, p. 829, and Non-Patent Document 4). Non-Patent Document 1, for example, discloses a technique for improving the communication speed by providing a plurality of transformers and forming a plurality of channels in parallel.
Alternatively, a technique which improves the communication speed by raising the self-resonant frequency of the inductor, is conceivable.